The advent of self-contained underwater breathing (SCUBA) gear has provided swimmers with a capability of performing valuable military assistance in such areas as sabotage, reconnaisance, and clearance of obstacles which will prevent or hinder small landing craft. During the second World War, for example, frogmen were credited with sinking large tonnage of ships by attaching explosive devices to the sides and bottoms of ships. In order for a frogman or swimmer to be effective, it is necessary for him to remain undetected for a man in water is not capable of effective combat with someone on the surface, either on land, air, or on a ship. Thus a frogman relies mainly on darkness and camouflage to escape detection.
Various items also float in water and any automatic detection device should be able to discriminate between a person and other objects, such as floating logs. This detection might be based on size, contract, speed of movement, and the like. Devices that can discriminate between various shapes of items are known in the art and, likewise, devices that discriminate or measure the contrast within an item are known. For example, in U.S. Pat. No. 3,529,169, which issued Sept. 15, 1970, to Richard Heaney et al, there is shown a device for detecting the shape of a ware, such as a bottle. In this device, light is projected through a rotating ware and the ware profile in the form of a shadow is cast on an array of light responsive devices. Such a shadow represents the configuration or profile of the ware. The array of light responsive devices, in turn, are arranged to detect both inward and outward deviations from a standard or desired shadow profile or a desired configuration of the rotating ware. Ware with no distortion or configuration defect will have a stationary pattern or a preselected shadow profile. On the other hand, a ware with distortion or with a configuration defect will produce a moving shadow or a nonconforming shadow profile. It is the array of light responsive devices that detects whether the configuration of the rotating ware conforms to preselected conditions and controls the operation of a decision circuit for either signaling the reject or accept status of the rotating ware or for controlling the operation of a reject or accept device disposed in the path of travel of the ware after the ware leaves the inspection station.
In U.S. Pat. No. 3,154,625, which issued Oct. 27, 1964, to James H. Kail, there is shown a device for grading meat by measuring the amount of fat in a cut. In this method, light is reflected from a cut of meat into a photometer which is adapted to register light reflected from fat but not to register light reflected from muscle. The percentage of fat present in the cut is used to grade the cut of meat.